Purification of interpolymers



atented June 15, 1943 STATES PATE'T Robert M.

Thomas, Union,

Lightbown, Roselle. N. assignments, to Jasco,

ration of Louisiana and Irving E. J.. assignors, by mesne Incorporated,a corpo- No Drawing. Application July 1, 1939, Serial No. 282,478

12 Claims.

mixtures of isoolefinic and diolefinic substances I into polymericsubstances which have many of the physical properties of rubber, such asa high elasticity; and when suitably cured have a high tensile strengthand high abrasion and flexure resistance as well as high chemicalresistance to chemical reagents as is shown in the copendingapplication, Serial No. 182,252, filed December 29,

1937, for one of the inventors of the present application, Robert M.Thomas. together with Willlam J. Sparks.

In the preferred form of the embodiment an isoolefln such as isobutylenemay be polymerized with small proportions of one or more dioleflns suchas butadiene, isoprene, cyclopentadiene, di-

methyl butadiene, etc., the diolefin beingpresent in relatively smallproportions ranging from part with 99 /2 parts of the isoolefin, to 30parts with 70 parts of isoolefin, to produce a polymer substance whichdiffers from the polymer produced from an isoolefin alone by thecapability of absorbing small proportions of sulfur to produce amaterial which can be cured by heat, and which when cured issubstantially lackin in cold flow, is insoluble in hydrocarbons and-hasa high tensile strength, as well as the other above-mentioned valuablephysical and chemical properties. By proper choice of catalyst such asaluminum chloride or zirconium tetra chloride dissolved in an alkylhalide solvent such as methyl or ethyl chloride and suitable choice oflow temperature,

ranging from about 0 C. to about -150. C; or

even lower,.it is possible to produce polymeric msterial havingmolecular weights ranging from 20,000 to 200,000 or above, the upperlimit being as yet unknown. These high molecular weight polymers maythen be mixed with various amounts of sulfur, zinc oxide and a smallpercentage of a suitable sulfurization catalyst such as approximately0.25 to 2.5% of Tuads (tetra methyl thiuram disulfide) and thereaftercured by heat to incorporate the sulfur into the polymer at temperaturesranging approximately from 120 C. to 180 C., preferably 150 C., forperiods of time ranging from 20 to 160 minute Itis found, however, thatsome batches of the polymeric material develop flaws or bubbles or weakspots within the bodyof the cured compound which seriously weakenthematerial and produce a very great decrease in tensile strength. eachbubble serving as a focal point for concen-- trationof stresses.

The present invention providesa simple procedure for overcoming thetendency to produce bubbles during the curing operation, and is alsoconcerned with a particular method of accomplishing the same, namely asolution and reprecipitation procedure in a particular type of solvent'by which procedure the bubble-produci substances are removed.

' Thus an object of the invention is to polymerize a mixture ofisoolefinic and diolefinic substances to produce a high molecular weightpolymer; thereafter to dissolve-the polymer in a solvent, and separatefrom the solution a desired portion of the dissolved polymer, which iscapable of being mixed with sulfur and sulfur compounds and cured byaheat treatment to avoid the development of bubbles and weaknessestherein, and to produce instead a fully homogeneous product.

Other objects and details will be apparent from the followingdescription:

In the operation of the refining of crude oil, it is customary to top"the crude to remove the natural gasoline, and thereafter to crack there-- sidual crude at high temperature and pressure for the production ofadditional quantities of gasoline boiling range hydrocarbons. Thiscracking operation .ous by-product, which consists in in part ofethylene and its homologues,

part of hydroincludin isobutylene, butadiene and similar isooleflnic anddioleflnic gases. The isoolefinic materials and the dioleflnic materialsare then separated from the cracking gases, and utilized for .the p e ofthe present invention.

The isoolefln such as isobutylene in the proportion of to parts isdesirably mixed with the diolefin such as butadiene in a. proportion of30 to 10 parts, this proportion applying particularly to mixtures ofisobutylenev and butadiene. A similar mixture may be prepared with to 99parts of isobutylene and 5 parts to 1 part of isoprene.

These mixtures of olefinlc gases are then chilled to temperaturesranging from about 50 produces also about 15% of gasein part of methaneand its homologues, and

C. to about -150 C. and mixed with a suitable diluent-refrigerant suchas liquefied ethylene, or liquefied propane, or other liquid mixtureswhich may include ethane and methane as well as the gases abovementioned. The mixture is polymerized with a catalyst which desirablyconsists of aluminum chloride dissolved in ethyl or methyl chloride, butmay also consist of zirconium tetra chloride or other active halidecompounds dissolved in suitable inert solvents of low freezing point asdesired.

The polymerization reaction occurs quickly to yield-the desired polymer,the heat of reaction being absorbed by the latent heat of vaporizationof the refrigerant-diluent which is desirably recondensed for recycling.It may be observed that in some cases. for example with isobutylene andbutadiene, the polymerization preferably does not go to completion, butthat a better product is obtained when the reaction product contains notmore than 40 to. 70% ot the mixed oleflnic materials. In all cases, theactivity of the catalyst is desirably destroyed at an appropriate stageoi the polymerization reaction by the addition thereto of a quenchingagent such as alcohol or other oxygenated compound.

The resulting polymer is then separated irom the reaction mixture andallowed to warm up to room temperature.

Ordinarily, the polymer so produced can be cured with small proportionsoi sulfur as above described, but shows a troublesome tendency towardthe development of bubbles in the mass of the cured material and inaddition is lacking in maximum physical strength, abrasion resistanceand flexure resistance.

Accordingly, by the added step or the present invention the polymer, asrecovered from the polymerization process, is dissolved in a solvent ofthe type ethylene dichloride.

Example 1 In this'procedure, the polymer material is dissolved in hotethylene dichloride at a temperature ranging between 60 C. and 100 C.,under pressure when the solution temperature is above the boiling pointof the ethylene dichloride at atmospheric pressure. It is found that thepolymeric material is soluble in the proportion of 95-100% in thesolvent at 84 C. temperature.

The ethylme dichloride is desirably saturated with polymer at thesolution temperature, and the solution is then separated from anyundissolved polymer or other residual materials. Upon terial is whollynon-crystalline and entire y,

amorphous it is not in fact an actual-,fractional crystallization.Furthermore, it may be observed that while a'iractional crystallizationis utilized for the purpose of separating diflerent chemical substances,the polymer broadly is a single chemical substance in which diiierentmolecules are of diiierent molecular weights. It is found that thehigher molecular weight molecules are less soluble in the ethylenedichloride than are the lower molecularweight molecules and accordinglythe first portion of the polymer to separate contains the highestmolecular weight polymer molecules. After the solution has cooled to asubstantially lower temperature such as C., the first separated portionof the polymer may be' removed. Thereafter a further portion may beobtained by further cooling of the ethylene dichloride solution, andsuccessive portions made up of progressively lower molecular weightmolecules may be recovered by successive separations at progressivelylower temperatures, until temperatures as low as 0 C. are reached. Attemperatures as low as this, substantially all of the solid polymericmaterial is separated. The ethylene dichloride may then be evaporated,and a residue of oily material which is polymer of molecular weightranging from approximately 500 to 2500 is secured.

It is believed that the oily material which does not separate from theethyl chloride solution by cooling is the corruptive factor whichproduces,

the bubbles and weakness of the polymeric material after curing sincerelatively minor difier- -ences only are found in the physicalproperties of trichlorethane, or various oxygenated compounds.

such as propyl or butyl ether, etc., and in certain'cases aromaticsolvents such as benzene or toluene. In other cases mixtures of suchsolvents with better solvents (e. g. CHCla or CClt) may be employed togive partial solvents for higher weight products.

Alternatively, the polymer materials may be dissolved in a suitablesolvent such as a low boiling hydrocarbon, or carbon tetrachloride, andprecipitated therefrom by a precipitant such as an oxygen-containingliquid of the type of the alcohols, acetones, ketones, etc., although ingeneral such a precipitation does not produce quite as sharp aseparation between the high molecular weights and low molecular weightsas does the 7 previous embodiment.

Example 2 In 10 liters of diisobutylene, grams of copolymer wasdissolved, and to this solution was added 10.5 liters oi'a solventmixture consisting of 50% by volume of 91% isopropyl alcohol and 50% byvolume oi. diisobutylene. After thorough mixing, 54 grams of a polymerhaving a molecular weight of 132,500 was precipitated. This precipitatewas recovered and dried. The product after compounding with sulfur andfillers and curing contained no blisters, whereas the directly curedproduct blistered badly.

Thus Example 1 discloses a procedure in which a moderately good solventfor the polymeric material is utilized as a medium in which a considerable proportion of polymeric material may be dissolved at a hightemperature and fractionally separated therefrom by successivereductions in temperature. This example is given as a representativeone, and the ethylene dichloride may be replaced by one or more of aconsiderable number of other solvents such as trichlorethane,perchlorethylene and suitable aromatic compounds such as benzene ortoluene.

On the other hand. Example 2 presents an embodiment of the invention inwhich a good sol-- vent tor the polymeric material is utilized, thesolution made at room temperature, and the vents and solventcombinations such as common oxygenated solvents, alcohols, ketones andlower ethe'rs such as isopropyl ether, ethyl ether, etc. The aboverepresentative embodiments utilize move solid impurities. Since,however, the polygood solvents for the polymer, and produce a truesolution which can be filtered if desired to remeric material asoriginally produced is usually a substantially free from such insolublesolid impurities, the filtration step is not always necessary.' 7

Accordingly, a third embodiment consists in a chemical extraction of theundesired portions of the polymer without the production of an actualsolution of all of the material. This embodiment'is" particularlyadvantageous with ultrahigh molecular weight material such as materialhaving an average molecular weight as produced in excess of 100,000 to200,000. Such material contains a large proportion of very highmolecular weight polymer which dissolves in any solvent only withconsiderable 'difliculty. However, by choice of an appropriate solventit may be swelled andthe lower molecular weight materials dissolved andextracted.

Example 3 For this purpose the polymer material may be treated withbenzene as a solvent. In this solvent 'the material swells andgoes intoa partial solution, the very high molecular weight material beingrelatively insoluble, and only the low molecular weight material beingsoluble to any substantial extent in the benzene. The polymer ma terialmay be treated with the benzene, and allowed to digest either at roomtemperature, or at elevated temperature, for a period of time rangingfrom 2 or 3- hours to several days. At the end of the digestion period,the soluble portion may be strained away from the insoluble portion. Theinsoluble portion then may be dried to volatilize traces of the solventwhich may have en-- tered the insoluble polymeric material. Polymericmaterial of sufficiently high average molecular weight to require thistype of treatment usually contains so little of the interferingsubstances that it will cure satisfactorily after a single extractiontreatment. If, however, a satisfactory cure is not obtained after asingle extraction treatment, the treatment may be repeated one or moreadditional times, using fresh solvent in each instance. Repeatedextraction will in most instances remove substantially all of theinterfering material and produce a polymeric product which is capable ofcuring to a high tensile' strength with entire freedom from flaws,bubbles and other strength-reducing defects.

The extraction may be accomplished at an elevated temperature, and if amoderate solvent of the type of ethylene dichloride is used, the veryhighest molecular weight portions of material may remain undissolvedeven at the elevated temperature. After the separation of the hotextractive solvent, cooling of the solvent will yield a substantialquantity of intermediate molecular weight material as in the embodimentof Example 1'; the thereafter addition of a precipitant such as amixture of isopropyl alcohol and diisobutylene will yield a quantity ofstill lower mo-' lecular weight polymer; and the evaporation ofthesolvent and precipitantwill result in the recovery of still lowermolecular weight, oily portions of polymer.

produced a new and useful pure polymer material which can be cured withsulfur without the production of flaws or bubbles or blisters in thebody of the material, and which has the new and outstandingly usefulcharacteristics of high tensile strength, high elasticity,higlnresistance to fiexure, high resistance to abrasion and highresistance to chemical substances generally.

While there are above disclosed but a limited number of embodiments ofthis invention, it is possible to produce still other embodimentswithout departing from the inventive concepts herein disclosed and it istherefore desired that only such limitations be imposed on the appendedclaims as are stated therein or required by the prior art,

The invention claimed is:

1. A sulfurizable material comprising an interpolymer of isobutylene anda conjugated diolefin having a molecular weight above 15,000 saidinterpolymer being free from fluid interpolymers of a molecular weightbelow about 2,500 which give rise to blister formation on curing byheating said interpolymer with sulfur.

2. A sulfurizable, polymeric material comprising a solid, plastic,substantially saturated, linear chain, high molecular weightinterpolymer of an isoolefin with a conjugated diolefin which is subamolecular weight below about 2 ,500.

3. In the processing of solid, plastic copolymerizates obtained by thepolymerization of an isoolefin with a conjugated diolefin in contactwith a solution of a Friedel-Crafts type catalyst at a temperaturebetween 50 C. and 6.,

the steps of segregating the copolymers into frac-' tions and separatingthe fractions of molecular weight below about 2,500 from the fractionsof higher molecular weight whereby the latter are rendered capable ofyieldingon curing products of high elasticity, high'tensile strength,high abrasion and flexure resistance substantially free from flaws,bubbles and blisters.

4. In the processing of solid, plastic copolymerizates obtained by thepolymerization of an isoolefln with a conjugated diolefin in contactwith a solution of a Friedel-Crafts type catalyst at a temperaturebetween 50" C. and 150 C., the steps of segregating the copolymers intofractions, separating the fractions of molecular weight below about2,500 from the fractions of higher molecular weight, compounding thelatter with sulfur andsulfur compounds and curing thematerial with theaid of heat to a strong, blisterfree condition.

5. In the processing of solid, plastic copolymerizates obtained by thepolymerization of an isoolefin with a conjugated diolefin in contactwith a solution of a Friedel-Crafts type catalyst at a temperaturebetween -50 and 150 C..'

the steps of dissolving a substantial portion of said copolymer andseparating the more dimcultly soluble copolymers having a molecularweight above 2,500 from the resultant solution.

6. In the processing of solid, plastic copolymerizates obtained by thepolymerization of an isoolefin with a conjugated diolefin in contactwith a solution of a Friedel-Crafts type catalyst at temperaturesbetween 50 and 150 C. to produce a solid, plastic interpolymer of theisoolefin and conjugated diolefin, the step of dissolving a substantialportion of the copolymer, separating the more diiiicultly solublecopolymers having a molecular weight above @500 from the I resultantsolution, compounding the said diiiicultly soluble copolymers withsulfur and sulfur compounds and curing the material with the aid of heatto a strong, blister-free condition.

7. In the processing of solid, plastic copolymerizates obtained by thepolymerization of, an isoolefln with a conjugated diolefln in contactwith a solution of a Friedel-Crafts type catalyst at a temperaturebetween -50 and 150 C.,-

the steps oi dissolving a substantial portion of said copolymerizate ina heated aliphatic compound capable of dissolving high' molecular weighthydrocarbons and separating the more dimcultly soluble copolymers from.the resultant solution by cooling, thereby obtaining the highermolecular weight copolymerizates .free from polymeric substances havinga molecular weightsteps of dissolving a substantial portion of saidcopolymerizate in a heated aliphatic compound capable of dissolving highmolecular weight hydrocarbons and separating the more diflicultlysoluble copolymers from the resultant solution into several fractions bycooling in successive,

stages. thereby obtaining the higher molecular stances having amolecular weight below 2,509 which interfere with the curing of thecopoly merlzates. 1

9. In the processing of solid, plastic copolymerizates obtained by thepolymerization of an isoolefin with a conjugated diolefln in contactwith a solution of a Friedel-Craits type catalyst at a temperaturebetween -50 and -150 C.- tbe steps of dissolving a substantial portionof said copolymerizate in heated ethylene dichloride mid separating themore diilicultly soluble copolymers from the resultant solution intoseveral fractions by cooling in successive stages, thereby obtaining ahigher molecular weight copolymerizate tree from polymeric substanceshaving a molecular weight below 2,500 which interfere with the curing ofthe copolymerizate.

10. In theprocessing of solid, plastic copolymerizates obtained by thepolymerization of an lsoolefin with a conjugated diqiefln in contact Aportion only of the polymer is soluble, separating the solvent andsoluble portion irom the insoluble with a solution of a Friedei-Craitstype catalyst at a temperature between -so and -150' (3.,

sistance substantially free mm flaws, bubbles and blisters; r

11. In the processing of solid, plastic copolymerizates obtained by..the, polymerization of an isoolefln witha .coniusa s dioleiin incontact with a solution of a Frledel-Craits type catalyst at atemperature between 50-and --'150 C.,

the steps of treating the polymerized material with an extractivesolvent in which a -iree from fluid polymeric substances having amolecular Weight below-2,500 andcaplble 0! yielding on curing withsulfur products oi high elasticity, high tensile strength, high abrasionresistance, and high flexure resistance substanwelght copolymerizamgfree from polymeric subs tially free from flaws, bubbles and blisters.

12. In the processing oisolid, plastic copolymerizates obtained by'thepolymerization ot-an isoolefln'with 8 conjugated dioleiln in Goliathwith a solution of ai'rledel-Crhtts type catalyst at a temperaturebetween 50 and l50 0.. the steps of treating. the polymerized materialwith benzene in suiiicient amount to dissolve a part only-oi thepolymerizate, separating the with suliur products of high elasticity, hih tensile stren th. high abrasion resistance flexure resistancesubstantially tree from flaws,

bubbles and blisters. I 4 ROBERT M. Thomas.

ravma n uon'raowu.

